This invention relates to an apparatus which may take the form of a stairway or pair of steps, the treads of which are always automatically maintained parallel to the ground regardless of the angle of the stringers relative to the ground. In consequence, when the apparatus is brought into a horizontal position, the treads form a substantially continuous plate.
Apparatus is already known which includes treads which are maintained horizontal regardless of the angle of the apparatus, such apparatus being used particularly for gangways connecting harbour quays with floating bridges or launches which are at a lower level than the quays but which are vertically movable with the rising and falling tide. With such apparatus it is not necessary for the treads to form a continuous plate intended for receiving a large load, and for the load to be distributed over substantially the entire length of the two stringers so that one stringer shall rest upon the other.
Ladders are also known, in which the stringers are pivotally mounted relative to a lower tread and a fixed, horizontal upper tread, as are ladders comprising a pair of fixed stringers, relative to which another pair is capable of being spread out or folded in.